Figure 9.14 (A) Posterior view of the long and lateral heads of the triceps brachii and the anconeus. (B) Posterior view of the medial head of the triceps brachii with the long and lateral heads of the triceps resected.
Humerus Lateral epicondyle
Radial collateral ligament Annular ligament
Supinator Ulna Radius Figure 9.15 Lateral view of the supinator muscle.
quadratus to rotate the radius around the ulna during forearm pronation. The pronator quadratus originates at the distal end of the forearm on the anterior surfaces of the ulna and radius. It produces forearm pronation and provides dynamic stabilization to the distal radioulnar joint (Fig. 9.16).
During many functional activities, forearm pronation and supination are associated with medial and lateral rotation at the glenohumeral joint. Shoulder lateral rota- tion is often paired with forearm supination, whereas medial rotation occurs with forearm pronation. Adding the rotary movement of the two joints allows the hand to perform tasks throughout approximately a 360° arc compared with the available 180° provided from supina- tion and pronation alone.
